Air-conducting ducts of this type are known, e.g. through U.S. Pat. No. 3,712,650 which issued to the same inventor on Jan. 23, 1973. The shape of such frame pieces is likewise known from this patent. The prefabricated glands are inserted on the front face of an air-conducting duct and then connected to the walls of the air-conducting duct with the aid of cross-connections. These cross-connections are usually spot-welding spots, but sometimes they are screws or rivets.
Two prefabricated glands each lie flush against each other, where a sealing strip is also added between their stays positioned perpendicularly to the duct wall.
The one gland may, however, not be prefabricated and belong, for example, to a ventilating appliance.
Such air-conducting ducts may have cross-section dimensions in the region of several decimeters to several meters. For reasons of sound insulation and/or heat insulation, it is sometimes necessary to cover the insides of the walls with insulating mats. Fastening of the mat to an extended part of the duct presents no considerable difficulty. The insulating mats usually have a relatively resistant skin on both sides and the material situated in between is very loose. With this skin, the insulating mats can be fastened, e.g. cemented to the inside of the walls.
The skin of the insulating mat cannot, however, be cemented at the point where the inner stay of the frame piece is situated. Nevertheless, they must be held there correctly from the point of view of flow technology, refrigeration technology and sound technology.